1. Field of the Invention
The present invention relates to a microcomputer having a function of monitoring a voltage, a hysteresis comparator circuit, and a voltage monitoring apparatus. More particularly, the invention relates to a microcomputer having a comparator for comparing a voltage to be monitored with a reference voltage, a hysteresis comparator circuit which can be mounted on the microcomputer, and a voltage monitoring apparatus for monitoring a voltage to be monitored.
2. Description of Related Art
In the field of vehicles and the like, there is a case that a microcomputer having a voltage comparator is used for monitoring a voltage of a battery or the like. For example, FIG. 7 of Japanese Unexamined Patent Application Publication No. 2005-71320 (patent document 1) shows a semiconductor integrated circuit device 51 including a microcomputer 55 which uses a comparator 67 for monitoring a power source voltage in an electric control unit of a vehicle. FIG. 9 of the patent document 1 shows that a comparator 73 is provided with a hysteresis characteristic.
Japanese Unexamined Patent Application Publication No. 2006-109013 (patent document 2) discloses an electronic control unit of a vehicle, having a comparator for a standby mode and a comparator for a normal mode, the comparators being coupled to same communication data (CAN), wherein a comparator switching circuit is provided which supplies different threshold voltages (reference voltages) to the two comparators and prevents a signal in an indeterminate level from being outputted at the time of mode switching between the standby mode and the normal mode.
Japanese Unexamined Patent Application Publication No. 2001-285038 (patent document 3) discloses a window comparator for determining whether input voltage lies in a predetermined voltage range or not.